1. Field of the Invention
The present invention relates to a laser processing machine suitable to form a process trench with a predetermined width, length and depth in the front surface of a workpiece such as a wafer or the like.
2. Description of the Related Art
For example, a printer head used in an inkjet printer is formed with an ink-holder trench measuring 30 to 200 μm in width, 10 to 15 mm in length and 100 to 200 μm in depth. Such an ink-holder trench is formed by etching, which is disclosed in e.g. U.S. Pat. Nos. 7,040,735 and 6,986,982. In order to form the ink-holder trench by etching, it is necessary to mask an area to be formed with no ink-holder trench in the front surface of a workpiece such as a wafer or the like. Thus, productivity is poor and it is difficult to sharply form the wall surfaces of the trench.
On the other hand, laser processing has been put into practical use as a productive processing method. A laser processing method is disclosed by Japanese Patent Laid-Open No. 2006-51517. In this method, a focusing spot is shaped ellipsoidal, the major axis of the ellipsoidal focusing spot is positioned along the processing line of a workpiece and the workpiece is transferred in the process transfer direction.
It is necessary to apply laser beams to one and the same position more than once in order to form a process trench with a predetermined depth by laser processing. The laser processing method described in the above patent document needs to transfer the workpiece by the distance corresponding to the length of the processing trench set in the process-transfer direction. Therefore, it needs to transfer the workpiece in the process-transfer direction the number of times necessary to process it to a preset depth. For this reason, it is limited to increase the process-transfer speed in view of the inertia force of a chuck table mechanism for holding the workpiece. Consequently, the laser processing method described above is not necessarily satisfied in view of productivity.